Medical device location systems, devices and methods

ABSTRACT

Methods, devices and systems for one or both of two- or three-dimensional location of the disposition of a sensor coil in a subject including: an array of electromagnetic drive coil sets, each set having two or three dimensionally oriented drive coils; a sensor coil being electromagnetically communicative with the array of electromagnetic drive coil sets; and, a system controller communicative with and adapted to energize one or more of the electromagnetic coils in the array of electromagnetic drive coil sets, the energizing of the one or more of the electromagnetic coils including one or more of energizing the coils singly, or in pairs of x-y and y-z or x-z coils, or in triplets of x-y-z coils while measuring the response of the sensor coil; whereby the system uses the measurements of the responses of the sensor coil to calculate the location and orientation of the sensor coil relative to said drive coil sets.

BACKGROUND

In medical care, the correct placement of a medical device such as acatheter or a guide wire in a patient has become increasingly importantfor a number of reasons. In the case of an infusion catheter, forexample, medications can need to be targeted to, or for, specificorgans, or areas of the body. A catheter can need to be locatedsufficiently near the heart in a particular region where there is aparticular blood flow rate; as for example, a particular high blood flowrate to ensure adequate dilution/mixing of infused fluids.Alternatively, a catheter or other internally-positioned medical devicecan simply need to be disposed in the right place to function; as forexample, an enteral feeding tube within the stomach. Use of a medicaldevice position location and/or guidance system can thus provide forless skilled practitioners to accurately and reliably position a medicaldevice such as a catheter.

Accordingly, a variety of systems have been developed to attempt toindicate location or position of catheters within the body of a patient.Relatively reliable location devices have made use of x-ray orfluoroscopy; however, these devices expose the patient and/or caregiverto undesirable amounts of radiation. As a consequence, a variety ofdifferent systems have been attempted to more continuously andaccurately indicate location of a catheter with a goal of replacing theuse of x-rays. However, such systems still suffer from various problems.

Electromagnetic catheter position location devices have been indevelopment. Some position location systems have made use of alternatingcurrent, AC, driven external coils with a sensor (sensor coil) in thecatheter tip. Others have used an AC driven coil in the catheter tipwith external sensor coils. A disadvantage of such a conventionalcatheter tip driven system has been the need for heavy or thick wiresrunning into the catheter to carry sufficient drive current to generatea sufficient electromagnetic signal for the external sensors. This hasprecluded the use of such a system with smaller diameter catheters.Other position location systems have used a fixed (or DC) magnet on thecatheter tip with external sensor coils. A significant disadvantage tosuch a fixed magnet location system has been that the magnet wouldnecessarily be very small, and as such would generate a very smallsignal from the tip of the catheter. As a consequence, other magneticfields in the vicinity can create significant interference problems forsuch a system. Furthermore, the field of such a magnet drops offextremely quickly over distance and thus cannot be sensed more than afew inches deep into the patient's tissue. Another AC drive system hasbeen described including driving two coils simultaneously; however,those respective coils were specified as having been driven at twodifferent frequencies so that the coil drives are not additive and thesensor demodulates the two different frequencies as two independentvalues. Yet another AC drive system has been described driving two coilssimultaneously in quadrature which simulates a single spinning coil;however, this system can only indicate the orientation of the sensor inthe x-y plane and its relative position in that plane.

This statement of background is for information purposes only and is notintended to be a complete or exhaustive explication of all potentiallyrelevant background art.

SUMMARY

Devices, methods and systems of the present developments can include asensor coil that may be associated with a medical device such as acatheter, this sensor coil being communicatively cooperative with, orresponsive to an array of drive coil sets of drive coils placed relativeto a subject's body to allow detection or positioning of the medicaldevice in the subject's body. Each of the drive coil sets and the sensorcoil may also be communicatively connected or cooperative with anexternal control and/or display box, for selective driving of the drivecoils of the sets of drive coils and for receiving response signals fromthe sensor coil.

Methods, devices and systems can be provided can be provided for one orboth of two- or three-dimensional location of the disposition of asensor coil in a subject including: an array of electromagnetic drivecoil sets, each set having two or three dimensionally oriented drivecoils; a sensor coil being electromagnetically communicative with thearray of electromagnetic drive coil sets; and, a system controllercommunicative with and adapted to energize one or more of theelectromagnetic coils in the array of electromagnetic drive coil sets,the energizing of the one or more of the electromagnetic coils includingone or more of energizing the coils singly, or in pairs of x-y and y-zor x-z coils while measuring the response of the sensor coil; wherebythe system uses the measurements of the responses of the sensor coil tocalculate the location and orientation of the sensor coil relative tosaid drive coil sets.

These and still further aspects and advantages of the presentdevelopments are illustrative of those which can be achieved by thesedevelopments and are not intended to be exhaustive or limiting of thepossible advantages which can be realized. Thus, these and other aspectsand advantages of these present developments will be apparent from thedescription herein or can be learned from practicing the disclosurehereof, both as embodied herein or as modified in view of any variationswhich can be apparent to those skilled in the art. Thus, in addition tothe exemplary aspects and embodiments described above, further aspectsand embodiments will become apparent by reference to and by study of thefollowing descriptions, including as will be readily discerned from thefollowing detailed description of exemplary implementations hereofespecially when read in conjunction with the accompanying drawings inwhich like parts bear like numerals throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic overview of present developments showing a usercontrol box, and a patient drive coil block with drive coil sets, and aguide wire or stylet with a sensor coil and cable.

FIG. 2 is a detailed view of one three-axis drive coil set.

FIG. 3 is a detailed view of a sensor coil.

FIG. 4 is an illustration of magnetic vectors generated by a normal coildrive.

FIG. 5 is an illustration of orthogonal magnetic vectors generated by anx-y virtual drive.

FIG. 6 is an illustration of orthogonal magnetic vectors generated by ay-z virtual drive.

FIG. 7 is a detailed view of a drive coil and sensor coil block with anaddition of an optional ECG measurement.

FIG. 8 is a block diagram of a present development hereof.

FIG. 9 is a block diagram of a display/interface and user control box.

FIG. 10 is a block diagram of a function of a main interface board in auser control box.

FIG. 11 is a block diagram of an overall function of a patient drivecoil block.

FIG. 12 a-12 f detail algorithms for controlling an acquisition ofsensor coil position optionally including display and/or ECG.

FIG. 13 is a detailed block diagram of a function of a coil drive withvirtual x-y capability.

FIG. 14 is a detailed block diagram of sensor coil signal processing.

FIG. 15 is a detailed block diagram of a function of a coil drive withfull virtual x-y-z capability.

FIG. 16 a-16 c detail some algorithm alternatives for controlling theacquisition and display of sensor coil position in virtual x-y-z system.

DETAILED DESCRIPTION OF FIGURES

FIG. 1 provides an overview of an implementation of a medical devicelocation system hereof. A user control box 20 may be included, andaccording to this implementation, contains a touch screen display 22, asingle-board computer (SBC) (not separately shown in FIG. 1) for controland data processing, and a main interface board (also not separatelyshown in FIG. 1) which connects to a drive block cable 26 and a medicaldevice cable 32 (also sometimes referred to as a catheter, or guide wireor stylet cable 32). A triangular patient drive coil block 36 may beconnected via drive block cable 26 to the control box 20 (the drive coilblock also sometimes being referred to as an emitter block, a patientblock or merely a drive block). Coil drive electronics 28 and threedrive coil sets 24 a, 24 b, 24 c (also sometimes referred to as emittercoils, or x-y-z drive coils) are mounted in the drive block 36. The coildrive electronics 28 allow the SBC to selectively energize any drivecoil axis 38, 40, 42 of a set 24 (see FIG. 2) or group of drive coilaxes. A sensor coil 30 is, in this implementation, built on or withinthe tip of a medical device such as a small diameter biocompatible guidewire or stylet cable 32. The guide wire may then be placed in thepatient and the catheter then threaded over this wire; or,alternatively, the stylet cable may then be inserted up to the distalend of a catheter before the catheter is placed in the patient. Atwo-conductor cable 34 can be used to connect the sensor coil of guidewire or stylet back to the user control box.

FIG. 2 shows a detailed drawing of a drive coil set 24 (representativeof any of sets 24 a, 24 b, 24 c). Here, the x-coil 42, the y-coil 38 andz-coil 40 each have a ferrite or ferrous core 44 to enhance the magneticfield generation. This figure is only schematically representative ofthe construction of a drive coil; in actuality, each drive coil may havemany windings (e.g. 100 turns) on the ferrite core and can beconstructed as three (3) coil pairs to facilitate the intersection ofthe x, y, and z axes. Each coil here has a set of lead wires 46 toconnect back to the multiplexers of the coil drive electronics 28.

FIG. 3 shows a detailed view of an exemplar medical device; e.g., aguide wire or stylet sensor coil. The sensor coil 30 can be any suitablegauge (e.g., but not limited to, a very fine gauge (e.g. 0.001″diameter)) insulated wire wound around a ferrous core wire 48. Thisfigure is schematically illustrative only of the sensor coil; here, thesensor coil is approximately 400 turns in single layer, but can be anysuitable turns per length, e.g., 50-1000, or any range or value therein,e.g., 100, 200, 300, 350, 400, 450, 500, 550, 600, 650, 700, and thelike. An alternative construction can optionally be 400 or more turns in2, 3, 4, 5, or more layers; here, the advantage of multiple even layersmay be the lead wires come off the same end of the coil. The sensor coillead wires 50 connect back through a cable to the patient isolatedportion of the main interface board. A thin insulating tubing 49 can beused to provide a protective sleeve for the whole assembly.

In an optional ECG version of a catheter location system (e.g., FIG. 7),the tip of the ferrous, conductive core wire 48 can be polished smoothand can provide an electrical signal as an ECG lead from within thecatheter. In such a version, the guide wire or stylet sensor connectionis accomplished with three wires, two (2) for the coil sensor and one(1) for the ECG, through a cable 54 to the patient isolated portion ofthe main interface board in the user control box 20. Furthermore, thepatient drive coil block 60 can have two ECG pads added which connectthrough a cable 62 to the patient isolated portion of the main interfaceboard. These two ECG inputs together with the one ECG from the catheterprovide a three-lead ECG measurement system (e.g., see FIG. 10).

FIGS. 4, 5 and 6 illustrate an optional version of the operation of anormal-drive and virtual-drive drive coil set. FIG. 4 shows magneticvectors x, y, and z generated by normal coil driving of the x-axis coil42, the y-axis coil 38 and z-axis coil 40 (as shown in FIG. 2). FIG. 5shows the virtual magnetic vector x-y generated by simultaneouslydriving the x-axis coil 42 and the y-axis coil 38 (as shown in FIG. 2)and when both are driven at the same power, the vector is forty-fivedegrees between the x and y axes. The virtual magnetic vector x-(−y)generated by simultaneously driving the x-axis coil 42 and thephase-inverted, y-axis coil 38 (as shown in FIG. 2) and when both aredriven at the same power, the vector is minus forty-five degrees betweenthe x and −y axes. If a digital to analog converter (DAC) is added tocontrol power to the x-axis drive and another DAC added to control powerof y-axis drive, then it is possible to point the virtual axis to anyangle from 0 to 360 degrees between x and y. For example, if x-axispower DAC is maximum and y-axis power DAC is ¼^(th) (one quarter) ofmaximum then the vector sum of x-y drive yields a virtual axis ofapproximately fourteen degrees between the x and y axes. FIG. 6 shows avirtual magnetic vector y-z generated by simultaneously driving thez-axis coil 42 and the y-axis coil 38 (as shown in FIG. 2); and avirtual magnetic vector z-(−y) generated by simultaneously driving thez-axis coil 42 and a phase-inverted, y-axis coil 38 (as shown in FIG.2). These figures illustrate the simplest and one optional form ofvirtual drive (e.g., see FIG. 13), it is possible to point a virtualmagnet vector to any polar coordinate by simultaneously driving x, y,and z coils at independent power levels (e.g., see FIG. 15).

FIG. 7 provides a schematic diagram of an optional medical devicelocation system with optional electrocardiograph (ECG) measurement. Thisis similar to the FIG. 1 implementation with the addition of three ECGleads. The user control box 20 connects through a main interface boardto the drive block cable 56 and guide wire or stylet cable 54. Thepatient drive block 60 may be connected via drive block cable 56 whichincludes two isolated ECG lead signals to the control box 20. The coildrive electronics 28 and three x-y-z drive coils 24 a, 24 b, 24 c may bemounted in the drive block 60. The coil drive electronics 28 allow thesingle board controller (SBC) to selectively energize any drive coilaxis 38, 40, 42 (FIG. 2) or group of drive coil axes. Two ECG pads 64are placed on the patient and connected by ECG lead wires 62 to thedrive block 60. The guide wire or stylet sensor 30 here is built onto asmall diameter biocompatible conductive-tip guide wire or stylet cable52 which is inserted into a catheter before (stylet) or after (guidewire) the catheter is placed in the patient. A three-conductor cable 54connects the guide wire or stylet sensor coil and one ECG lead back tothe user control box 20.

FIG. 8 is an overall schematic diagram of a medical device locationsystem. This figure illustrates connections between a user control box20 and a sensing guide wire or stylet 30 and a patient drive block 36,60. The control box 20 can include an integrated, separated, or remoteuser display and/or interface. Each of these components can includecables or connectors for one or more of a coil interface, a powersupply, a serial interface, a control interface, a status interface, anECG interface or lead, an oscillator interface, a processor interface, acomputer interface, a data interface, a network interface (cable orwireless), an internet interface, a video interface, a touch-screeninterface, an SBC control or power interface, a board interface, asensor interface, an isolator interface, and/or the like as describedherein or as known in the art. One or more of these cables or connectorscan attach to the patient drive block 36/60 or any component thereof.

FIG. 9 is a block diagram of a user control box 20 which in thisimplementation includes a computer 68, an LCD display 22 withtouch-screen, and a main interface board 70. Each of these componentscan include cables or connectors for one or more of a coil interface, apower supply, a serial interface, a control interface, a statusinterface, an ECG interface or lead, an oscillator interface, aprocessor interface, a computer interface, a data interface, a networkinterface (cable or wireless), an internet interface, a video interface,a touch-screen interface, an computer control or power interface, aboard interface, a sensor interface, an isolator interface, and/or thelike as described herein or as known in the art.

FIG. 10 provides a detailed block diagram of a main interface board 70(FIG. 9) and shows a patient isolated section which connects to a guidewire or stylet cable 34, 54 and an ECG leads from a patient drive block60. The remainder of the circuitry controls power/interface to a patientdrive block 36, 60 and power to a single board computer 68, includingone or more of a voltage regulator, a watchdog switch, a drive switch, apower isolator, a voltage monitor, a cable buffer, a filter, an analogto digital converter, a phase adjuster, a demodulator, a signal filter,a programmable gain amplifier, a coil isolator, a coil sensor coilamplifier, a detector, memory, flash memory, a multiplexor, a polarityinversion switch, and/or the like. Each of these components can includecables or connectors for one or more of a coil interface, a powersupply, a serial interface, a control interface, a status interface, anECG interface or lead, an oscillator interface, a processor interface, acomputer interface, a data interface, a network interface (cable orwireless), an internet interface, a video interface, a touch-screeninterface, an SBC control or power interface, a board interface, asensor interface, and/or the like as described herein or as known in theart. One or more of these cables or connectors can attach to a patientdrive block 36/60 or any component thereof.

FIG. 11 is a detailed block diagram of a patient drive block 36, 60(FIGS. 1, 7). A simpler version/option of a patient drive block 36 doesnot have ECG therefore no ECG leads; whereas, patient drive block 60 mayinclude two ECG leads with patient isolation. The drive coil drivesystem in this diagram illustrates a two-coil virtual drive capabilityallowing the computer software to simultaneously drive two coils atselect power levels. Such a system can include one or more of a voltageregulator, a watchdog switch, a drive switch, a power isolator, avoltage monitor, a cable buffer, a filter, an analog to digitalconverter, a phase adjuster, a demodulator, a signal filter, aprogrammable gain amplifier, a coil isolator, a coil sensor coilamplifier, a detector, memory, flash memory, a multiplexor, a polarityinversion switch, and/or the like. Each of these components can includecables or connectors for one or more of a coil interface, a powersupply, a serial interface, a control interface, a status interface, anECG interface or lead, an oscillator interface, a processor interface, acomputer interface, a data interface, a network interface (cable orwireless), an internet interface, a video interface, a touchscreeninterface, an SBC control or power interface, a board interface, asensor interface, and/or the like as described herein or as known in theart.

FIGS. 12 a-f provide an overview of a software functionality for amedical device location system hereof.

FIG. 13 is a simplified virtual coil drive system located on a patientdrive block 36, 60. A coil driver hereof may have only two coil drivesand only high/low power selection instead of a power control DAC. Inthis drive system it is possible to generate x-y and x-(−y) virtual coildrive (see FIG. 5) and also z-y and z-(−y) drive (see FIG. 6). Oneadditional feature of this drive is a low power setting which allowsdrive power reduction if the sensing coil is too close to the drive coil(see software flow chart FIG. 12 d). It also is possible to have twoadditional virtual vectors in this drive system by driving x-high-powertogether with y-low-power or driving x-low-power with y-high-power.Here, driving x-low-power together with g-low-power yields the samevirtual axis—forty-five degrees from x and y axes—as driving both athigh power.

FIG. 14 is a detailed view of the sensor coil processing system of themain interface board 68. The sensor coil 30 on the guide wire or styletcan be connected through a cable 34, 54 to the main interface board 68.This sensor coil input is pre-amplified and filtered then passed througha patient isolation transformer to a software-controlled programmablegain amplifier. This amplified signal is then demodulated using the lowfrequency (e.g. 16 kHz) drive oscillator. The software then reads thesensor coil value with a high resolution (e.g. 16 bit or higherresolution) analog to digital converter (ADC). This read value for eachdrive coil activated and this value is proportional to the magneticfield measured by the sensor coil during that drive coil activation.

FIG. 15 is a detailed view of a more complex virtual drive system. Thisdrive system allows the x-axis coil 42, the y-axis coil 38 and z-axiscoil 40 to all be driven simultaneously at independent power levels setby computer control through individual digital to analog converters(DAC). In this drive system, the virtual magnetic vector is the vectorsum of x-axis drive plus y-axis drive plus z-axis drive. This virtualdrive permits the virtual vector to point to any polar coordinate inspace, and thus use polar coordinates as an option; however, it mayoften still be preferable to use a set of three orthogonal “virtual”axes to calculate the sensor coil 30 position.

FIGS. 16 a-c are a software flow chart showing changes drive and sensorcoil processing for a fully independent x-y-z virtual drive system (seeFIG. 15). This software adds a positive offset test and a negativeoffset test to the virtual axes for the A-corner coils. If the sensorcoil response is stronger for an offset axis (FIG. 16 c) than thecurrent virtual axes, the system shifts to use the offset axes.

DETAILED DESCRIPTION

An aspect of the present developments is to provide an accurate systemto generate a three-dimensional indication of location, position,orientation and/or travel of a medical device such as a guide wire or acatheter or stylet placed within a patient. This can in someimplementations include a display of the location and/or travel of thedevice. A system hereof can include a sensor coil which is disposed inor on the tip of a guide wire or stylet cable, this sensor coil beingcommunicatively cooperative with an external control and/or display boxwhich may also be communicatively connected with an array of three-axisdrive coils placed in some implementations in a triangular block on thepatient's chest. This is also sometimes referred to as a drive block oran emitter block. The block contains the coil-drive controller thatfacilitates driving single coils, or pairs of coils, or triplets ofcoils together. The pair driving allows x-y, x-z, or y-z coils in acorner to be energized at the same frequency and same power creating avirtual drive axis at a 45 degree angle between the axis pairs. Thecoil-drive may also have an additional control to invert the drivewaveform (shift the phase 180 degrees). This inversion of one coil inthe pair can create a virtual drive axis at −45 degrees, thus creatingan orthogonal pair of virtual axes within a plane. For example, thevirtual x-y and x-(−y) are in the same plane as the x and y axes butrotated 45 degrees within the plane. This paired drive scheme improvesthe measurement accuracy of the system, especially when the sensorinside the catheter tip is substantially or exactly perpendicular to anormal coil drive axis. The system controller sequentiallydrives/energizes each coil, then each pair of coils while measuring thesensor coil response. When the sensor coil is nearly perpendicular to adrive axis there is significantly diminished response; thus, the virtualaxis measurement will provide more accurate data for the positionalgorithm. Algorithms within the controller can be used to select thebest data sets—regular x-y-z axis or virtual x-y-z axis—to calculate thesensor/medical device (e.g., catheter tip) location, position and/ororientation. A display can be used to show the catheter tip location asa position track of x-y location plotted over time plus an indicator forthe z-axis, depth of the catheter. Depth could also be indicated by avariety of methods, as for example by thickening the position linesegment in the plot as z decreases and thinning the position linesegment as z increases. Alternatively, depth can be displayed as alateral or “depth” view as a position track of y-z location plotted overtime.

It is possible to extend this system further using programmable currentcontrol to the coil-driver circuit. Here, a virtual axis could becreated at any angle between a magnet pair in a corner by energizing twomagnets at the same frequency but with different current drive (power)levels to yield a vector-sum virtual axis at any angle between 0 and 90degrees and inverting one coil in this drive scheme to yield avector-sum virtual axis at any angle between 0 and −90 degrees. However,an orthogonal set of axes would typically still be selected toaccurately locate the sensor coil. A further extension to this systemcould include energizing all three electromagnetic coils, x-y-z,together in a corner using the programmable current controls andinversion controls. The result here would be a vector sum from x-drive,y-drive, and z-drive coils that creates a virtual drive at any vectorwithin three-dimensional space.

It is also possible to enhance this system with the integration ofelectrocardiogram (ECG) display with the location system. Here tworeference electrodes may be plugged into or otherwise connected to thetriangular patient block with the third electrode connected to thestylet or guide wire. An ECG may then be displayed for the user, so thatP-wave changes, or other waveform changes can be shown to indicateproximity of the stylet or guide wire to the heart.

An aspect of the present developments is an electromagnetic medicaldevice locating system for locating a medical device or the end or thetip thereof in a subject, including one or more of:

-   -   three or more triplet drive coil sets, each drive coil set        including at least three orthogonally arranged discrete drive        coils, each of the discrete drive coils being electromagnetic        (EM) coils;    -   at least one sensor coil;    -   one or more system components that one or both provide drive        signals energizing said discrete drive coils and measure        resulting sensor coil response signals;        wherein the provision of drive signals includes one or both:    -   (i) sequentially driving one or pairs of said discrete drive        coils within a triplet drive coil set; and    -   (ii) selectively providing phase inversion of the drive signal        to any one or pairs of said discrete drive coils within a        triplet drive coil set;    -   a computing component for calculating sensor coil disposition in        the subject relative to said triplet drive coil sets from one or        more measured resulting sensor coil response signals.

Another aspect may include: (a) three or more virtual or actual x-y-zaxis electromagnetic (EM) triplet drive coils, each including at leastthree virtual or actual EM drive coils arranged in perpendicular axis toeach other along an x-y-z axis, the virtual or actual EM triplet drivecoils placed in a two- or three-dimensional geometric array; (b) atleast one medical device sensor coil in physical association with atleast one medical device tip and connected to at least one demodulatorcircuit; (c) at least one AC drive controller that (i) drivessequentially one or more of the virtual or actual EM drive coils; and(ii) provides a phase shifted signal to the demodulator; (d) at leastone demodulator circuit including at least one demodulator for measuringthe sensor coil output signal using frequency correlation with at leastone AC coil driver signal from the AC drive controller to provide asynchronously demodulated sensor coil signal; (e) at least one automaticgain control circuit that maximizes the demodulated sensor coil signal;(f) a computing component for normalizing the resultant demodulatedsensor coil signal data by dividing or multiplying the determinedprogrammable gain value from the measurement of the demodulated sensorcoil signals; (g) a computing component for selecting and calculatingthe optimized demodulated sensor coil signal data set generated fromdemodulated sensor coil signals, which optimized coil signal data set iscalculated based on the sum of measured squared terms that haverelatively higher or highest values; (h) a calculator for calculatingthe distance of the sensor coil and medical device tip from three ormore virtual or actual EM triplet drive coil locations using theoptimized demodulated sensor coil data set calculated using intersectionof the spheres to provide the location of the sensor coil andcorresponding medical device tip in space relative to the location oftwo or more of the virtual or actual EM triple drive coils provided inthe two- or three-dimensional geometric array corresponding to thelocation of the medical device tip in the subject; and in someimplementations, (i) a display. The result is the actual location of themedical device tip in the subject indicating height, width, and depth ofthe medical device tip in the subject calculated relative to theposition of the drive coil geometric array.

It is possible to extend this system to include wherein one or more of(i) the virtual or actual EM drive coils or the virtual or actual EMtriplet drive coils are arranged outside at least one of a twodimensional plane defined by at least three of the virtual or actual EMtriplet drive coils; and/or (ii) at least four of the virtual or actualEM triplet drive coils form a tetrahedron as part of thethree-dimensional geometric array.

It is possible to enhance such a system to include one or more ofwherein (i) the display displays the relative location of the sensorcoil or the medical device tip as a tracking of the sensor coil ormedical device tip location over time; (ii) the display displays thesensor tip angle graphically for the user of the system, wherein themedical device tip angle is the angle of maximum response of the sensorcoil as measured from sweeping the virtual drive axis through x-y plane(e.g. 0 to 360 degrees) then using this x-y maximum response angle as avector added to the sweep through the virtual z axis; and/or (iii) thedisplay displays the sensor tip angle graphically for the user of thesystem, wherein the medical device tip angle is the angle perpendicularto the angle of minimum response of the sensor coil as measured fromsweeping the virtual drive axis through x-y plane (e.g. 0 to 360degrees) then using this x-y minimum response angle as a vector added tosweep through the virtual z axis.

It is possible to extend such a system to further include wherein theintensity or power of current running through one or more adjacent EMdrive coils in at least one of the EM triplet drive coils isprogrammable or adjustable using a control box including a programmablecomputer.

An aspect of the present developments is to provide a system wherein oneor more of the EM drive coils are provided as the virtual EM drivecoils, and wherein: (a) one or more controllers that select pairs ortriplets of drive current values of the EM drive coils at regular timeintervals to provide one or more paired magnetic drive coil vectorvalues at angles from 0 to 90 degrees and phase inversion of at leastone of the corresponding EM drive coils in at least one pair of thepaired or tripled magnetic drive coil vectors to further provide one ormore magnetic drive coil vector values at angles from −90 to 0 degrees;(b) one or more controllers that: (i) determine the angle values ofmaximum and minimum sensor coil responses within a plane using pairedcoil programmable current drive sweeping a range from 0 to 90 degrees;and (ii) that then determine the angle values of maximum and minimumsensor coil responses within a plane using paired coil programmablecurrent drive sweeping using inverted phases of at least one coil andsweeping a range from −90 to 0 degrees; and/or (c) a calculator that:(i) computes at least one set of optimal virtual drive x and y axes forat least two of the EM triplet drive coils as values corresponding toplus and minus 45 degrees from the maximum and minimum sensor coilresponses; and (ii) computes an optimal virtual drive z axis orthogonalto the plane of the optimal virtual drive x and y axes to provide atleast one optimal virtual EM triplet drive axes and at least one of thevirtual EM triplet drive coils.

Such a system can be extended wherein the system includes a programmablecoil drive current for each of x, y, and z drive coils driven; andwherein (a) the triplets of drive current values selected at regulartime intervals are provided as (i) paired magnetic drive coil vectorvalues at angles from 0 to 90 degrees in an x-y plane together with 0 to90 degrees from the x-y plane to the corresponding z-axis; and (ii) asphase inversion of one or two paired magnetic drive coil vector valuesat angles from −90 to 0 degrees in an x-y plane together with from −90to 0 degrees from the x-y plane to the corresponding z-axis; (b) theangle values of maximum sensor coil responses within a plane for both 0to 90 and −90 to 0 degrees are fixed and used for at least two x and yvirtual axes in a virtual plane and the values of maximum sensor coilresponse are determined for the corresponding virtual z axis to provideat least one maximum virtual x-y-z vector for at least one of thecorresponding virtual EM triplet drive coils; (c) the angle values ofminimum sensor coil responses within a plane for both 0 to 90 and −90 to0 degrees are fixed and used for at least two x and y virtual axes in avirtual plane and the values of maximum sensor coil response aredetermined for the corresponding virtual z axis to provide at least oneminimum virtual x-y-z vector for at least one of the correspondingvirtual EM triplet drive coils; (d) the at least one optimal virtual EMtriplet drive vector and at least one of the virtual EM triplet drivecoils are generated using intermediate virtual drive x and y axes asplus and minus 45 degrees from the minimum virtual x-y-z vector andintermediate virtual drive z axis as orthogonal to the intermediatevirtual drive x and y axis; the optimal virtual x, y, and z axis arethen generated by pivoting the intermediate x, y, and z axes by movingthe intermediate z axis 45 degrees about the maximum virtual x-y-zvector.

Such a system can be enhanced wherein the display further displaysP-wave or other cardiac waveform changes over time in combination withthe location of the medical device such as a guide wire or stylet tip inrelationship to the subject's heart.

Such a system can be extended by further including (i) an x-axis tiltmeter and y-axis tilt meter which uses gravity to measure the x-axis andy-axis tilt from true vertical; and (2) a computer to calculate anddisplay the location of the medical device tip as height, width, anddepth of the sensor coil corrected for the tilt the geometric array.Such a system can be enhanced wherein the geometric array and sensorcoil connected to the display via a wireless interface.

Such system can be extended by further including an electrocardiogram(ECG) operably associated with the geometric array with a display toshow the subject's ECG signal over time; or by further including anelectroencephalogram (EEG) operably associated with the geometric arraywith a display to show the subject's EEG signal over time.

An aspect of the present developments can include a method for locatinga medical device in a subject, including: (a) providing a system aspresented herein; (b) inserting and positioning the medical device tipassociated with a functional and sterile medical device into thesubject; and (c) recording or monitoring the output of the display tolocate the medical device tip in the subject.

Such a method can be extended wherein the method further includes theuse of at least one selected an electrocardiogram (ECG), anelectroencephalogram (EEG), an x-ray machine, an computer assistedtomography (CAT) machine, a positron emission tomography (PET) machine,an endoscope, or an ultrasound imaging device or composition.

Methods, Computer Systems and Software

An aspect of the present developments can include methods, computersystems and software, provided as programming code or instructions oncomputer readable media or hardware or networks or computer systems, forgenerating virtual electromagnetic (EM) triplet drive coils forgenerating data corresponding to the location coordinates for a sensorcoil, including:

-   -   (a) electronically providing triplets of drive current values        generated from at least three EM drive coils of the EM triplet        drive coils in detectable proximity to the EM sensor at regular        time intervals to provide one or more paired magnetic drive coil        vector values generated at angles from 0 to 90 degrees without        and from −90 to 0 degrees with phase inversion;    -   (b) electronically providing angle values of maximum or minimum        EM sensor coil responses generated from the EM triplet drive        coils within the x-y plane using paired x-y coils' programmable        current drive sweeping a range from 0 to 90 degrees without and        from −90 to 0 degrees with phase inversion;    -   (c) electronically computing at least one set of optimal virtual        drive x and y axes as values corresponding to plus and minus 45        degrees from the maximum or the minimum sensor coil response;    -   (d) electronically computing an optimal virtual drive z axis        orthogonal to the plane of the optimal virtual drive x and y        axes to provide at least one optimal set of virtual EM triplet        drive axes for at least one of the EM triplet drive coils.

Such a method can be extended wherein (a) the triplets of drive currentvalues selected at regular time intervals are provided as (i) pairedmagnetic drive coil vector values at angles from 0 to 90 degrees in anx-y plane added together with coil vectors of the z-axis from 0 to 90degrees from the x-y plane; and (ii) as phase inversion of one or morepaired magnetic drive coil vector values at angles from −90 to 0 degreesin an x-y plane added together with coil vectors of the z-axis from −90to 0 degrees from the x-y plane; (b) the angle value of maximum sensorcoil response within the x-y plane for both 0 to 90 and −90 to 0 degreesis determined as the intermediate virtual maximum x-y axis and thisintermediate virtual maximum x-y axis added to the z-axis swept from 0to 90 and −90 to 0 degrees to determine at least one maximum virtualx-y-z vector for at least one of the corresponding EM triplet drivecoils; (c) the angle value of minimum sensor coil response within thex-y plane for both 0 to 90 and −90 to 0 degrees is determined as theintermediate virtual minimum x-y axis, and this intermediate virtualminimum x-y axis is added to the z-axis swept from 0 to 90 and −90 to 0degrees to determine at least one minimum virtual x-y-z vector for atleast one of the corresponding EM triplet drive coils; and (d) the atleast one optimal virtual EM triplet drive axes for at least one of theEM triplet drive coils are calculated using plane defined by the maximumvirtual x-y-z vector and minimum x-y-z vector wherein the optimalvirtual drive x and y axes are plus and minus 45 degrees from theminimum virtual x-y-z vector and the optimal virtual drive z axis asorthogonal to the optimal virtual drive x and y axes.

FIG. 1 is an overview schematic diagram of an implementation of thepresent developments. A control box 20 contains a touch screen display22 with a computer control and data processing. The triangular patientdrive block 36 is connected via power and communications cable 26 to thecontrol box 20. The drive and sensor electronics 28 may be located inthe block 36 and provide drive coil control and sensor coildemodulation/amplification. In the three corners of the block 36 aremounted each triplet drive coil set 24 (24 a, 24 b, 24 c).Alternatively, each coil set 24 could be mounted as feet protruding fromthe bottom of the block 36. The sensor coil 30 is built onto a smalldiameter biocompatible cable 32 which may be inserted into a medicaldevice such as a catheter to be placed in the patient. The sensor signalis connected back to the control box 20 with a two-wire cable 34. FIG. 3provides a detailed view of a sensor coil 30. Sensor coil performancecan be improved by winding the coil about a ferromagnetic wire in thetip of the cable 48. The ferromagnetic material should be used for thelength of the sensor coil 30 and may be followed by non-ferrousmaterial. Two fine wires 50 from the sensor coil 30 are attached orassociated (e.g., glued or wrapped) and sealed 49 down the length of thecable 48.

As presented, e.g., in FIG. 8, an aspect of this device may includecontinuous display at the position of the sensor coil 30 placed in thetip of a medical device as the medical device moves through thepatient's tissue. The patient drive block 36, 60, is placed over thepatient's body where the medical device will be targeted (e.g., over thechest preferably aligned with the sternal notch if the medical devicewill be placed in the area of the heart).

As presented, e.g., in FIG. 1 and FIG. 7, respectively, the sensor coilcable 34, 54 and patient drive block cable 26, 56 are connected to auser control box 20. The user control box 20 contains a computer 68(FIG. 9) which sequentially drives each driver coil 38, 40, 42 (FIG. 2)on each axis in every corner 24 a, 24 b, 24 c of the patient drive block36, 60. The coil driver creates magnetic drive vectors as shown in FIG.4, 5, or 6—where FIG. 4 represents normal drive and FIGS. 5 and 6represent virtual drive. The single board computer 68 (FIG. 9) measuresthe demodulated output signal from the sensor coil 30 for eachsequentially driven coil 24 (FIG. 1). The single board computer 68 (FIG.9) continuously adjusts the gain of each output signal using aprogrammable gain stage in the demodulator electronics and scales allthe sensor data to be gain normalized (see FIG. 12 b). Here, gainnormalized means that if a measured response is value “a” collected at aprogrammable gain of “4.00” times, then the normalized resultant valueis “a” divided by 4.00. A non-limiting example of an alternative gainnormalizing method is to multiply each value “a” by 4096/gain, e.g.“a”×4096/4.00. The programmable gains that can be used as a non-limitingexample are 1.00, 2.00, 4.00, 8.00, 16.00 and 32.00 plus there can be afinal gain stage that is selectable for 1.00 or 1.41 (equivalent to1/√2). Examples of a resultant set of programmable gains are 1.00, 1.41,2.00, 2.82, 4.00, 5.64, 8.00, 11.28, 16.00, 22.56 and 32.00.

From the normalized response data, the single board computer 68 (FIG. 9)compares the sum of the squares of the sensor's normal response to thesum of the squares of the sensor's virtual response. Whichever sum isgreater or has the stronger response can be used by the computer 68 tocalculate the sensor coil 30 location using trilateration which is thecalculation of the intersection of three spheres where each sphere isdefined as the radial distance of the sensor coil 30 from each x-y-zdriver coil set 24 a, 24 b, 24 c (FIG. 1).

From each corner, the radial distance can be defined as a constantdivided by the 6^(th) root of the sum of the squares of the x, y, and zmeasured normalized response. Here the constant, k, is a calibrationconstant reflecting the strength of each drive coil 38, 40, 42 (FIG. 2)and the sensitivity of the sensor coil 30 (FIG. 1). In one possibleaspect, a calibration constant could be generated during manufacturingfor each of the drive coils and then stored as calibration constants foreach coil in non-volatile memory of the patient drive block. Bytrilateration, the radial distance equation for each corner is:r=k/ ⁶√((x ² +y ² +z ²))

The sensor coil location is then calculated from three equations for thethree corners of plate 36:r ₁ ² =k ²/³√((x ₁ ² +y ₁ ² +z ₁ ²))r ₂ ² =k ²/³√((x ₂ −d)² +y ₂ ² +z ₂ ²)r ₃ ² =k ²/³√(x ₃ ²+(y ₃ −d)² +z ₃ ²)Here d is the distance of each coil from the other and k is thecalibration constant which scales the result into meaningful units ofdistance, e.g. centimeters or inches. In this non-limiting example, thecoils on the patient drive plate or block 36, 60 (FIGS. 1 and 7) arearranged in a right triangle, with two sides of equal length, d, asreflected in the 2^(nd) and 3^(rd) equations above, just on differentaxis, x or y. The solution to these equations yielding the sensor coillocation is:x _(S)=(r ₁ ² −r ₂ ² +d ²)/2dy _(S)=(r ₁ ² −r ₃ ² +d ²)/2dz _(S)=+/−²√(r ₁ ² −x _(S) ² −y _(S) ²)Here the solution for z (vertical axis) is assumed to be negative as thesensor coil 30 cannot be above the plane of the patient drive block 36,60 (FIGS. 1 and 7) unless it is outside the patient.

While the above reflects one non-limiting approach to locating thesensor coil 30 (FIG. 1), it is not the only or optimal for coillocation. Specifically when the sensor coil 30 is nearly perpendicularto a driver coil axis the sensor coil response approaches zero;therefore a “virtual axis” drive system provides for the optimal sensorcoil response. In this approach the coil driver circuit is designed toselectively drive, within a triplet set, pairs of coils, e.g. 38 and 42(FIG. 2), together at the same frequency and amplitude with anadditional driver control to selectively invert the phase of one coil inthe pair. This paired coil drive of x-y coils creates the 1st virtualaxis at forty-five degrees from the original x and y axes. The pairedcoil drive is then operated with x-(−y) which drives the x-coil togetherwith inverted-phase y-coil and this creates the 2^(nd) virtual axis atminus forty-five degrees from the original x and y axes. The result istwo orthogonal virtual magnetic vectors as shown by the dashed lines inFIG. 5 for x-y paired coil drive or in FIG. 6 for y-z paired coil drive.For paired drive, the single board computer 68 (FIG. 9) sequentiallydrives the x-y pair, x-(−y) pair, and z axis for each x-y-z coil set 24a, 24 b, 24 c (FIGS. 1 and 7). Here, “(−y)” means inverted phase on yaxis drive. The measured sensor coil response for paired-coil drive mustbe scaled down by 1.4142 because of vector summing of the two coilsdriven together. Alternatively, the coil-driver power could be scaleddown by 0.7071 in hardware when driving pairs so that the vector sum oftwo coils equals the magnetic vector of a single coil drive. The singleboard computer 68 measures the sensor coil response for each corner innormal drive and paired drive, and then selects the strongest signalfrom each corner comparing the sum of x², y², and z² normal coil driveresponse to the sum of (x-y)², (x-(−y))², and z² paired coil driveresponse. The strongest signal from each corner is used to calculate thelocation of the sensor coil 30 using the trilateration method describedin the above equations. This example illustrates paired x-y coil drive;and by logical extension this may also apply to x-z, or y-z paireddrive. An objective in some implementations of these developments mayinclude improving the accuracy of horizontal (x-y) location; thereforethe paired x-y drive can be preferred over x-z or y-z.

An improvement of the paired-coil drive can be to add programmable (DAC)power control to the coil drivers on the drive coil drive electronicsboard 28 (FIG. 11). Here, the single board computer 68 (FIG. 9) has thecapability to select pairs of drive current power settings which steerthe virtual axis of the paired coils from 0 to 90 degrees. Inversion ofone of the coil drivers in the pair provides the capability for virtualaxis from −90 to 0 degrees. In this design, the single board computer 68selects pairs of power settings output to the x-y paired coil driver tosweep the virtual drive axis from 0 to 90 degrees while recording thesensor coil response and this process is repeated with the y coil driverphase inverted to sweep from −90 to 0 degrees. The angle of the virtualaxis when the sensor coil response data is maximum indicates the sensorcoil 30 (FIG. 1) is parallel to the virtual axis and the angle of thevirtual axis when the sensor coil response data is minimum indicates thesensor coil 30 is perpendicular to the virtual axis. Here the maximumangle and minimum angle are orthogonal (perpendicular). The single boardcomputer 68 (FIG. 9) calculates the optimum virtual x axis at forty-fivedegrees from the measured angle for maximum (or minimum) response andcalculates the optimum virtual y axis as an angle orthogonal to thevirtual x axis. As all x-y-z coil sets 24 a, 24 b, 24 c are mechanicallyaligned the solution for best virtual axes in one corner applies to allcorners in the patient drive block 36, 60 (FIGS. 1 and 7). The singleboard computer 68 (FIG. 9) measures the sensor coil response for allcorners using these optimum virtual x axis, optimum virtual y axis plusnormal z axis. The sum of (virtual x)², (virtual y)², and z² sensor coilresponses for each corner is used to calculate the position of thesensor coil 30 (FIG. 1) using the trilateration method described in theabove equations. This example illustrates paired x-y coil drive; and bylogical extension this also applies to x-z, or y-z paired drive;however, the preference in this development is to improve accuracy ofhorizontal location and thus use paired x-y drive.

An alternative, non-limiting, method for finding the optimum virtual xand virtual y axis in the programmable pair-coil drive above is to usesuccessive approximation instead of sweeping 0 to 90 degrees. In thisapproach, the single board computer 68 (FIG. 9) has the capability toselect pairs of drive current power settings which steer the virtualaxis from −90 to +90 degrees. The single board computer first tests thesensor coil response to the paired coils at virtual axes +45 and −45degrees and selects the virtual axis with the stronger response. Usingthe stronger axis, the computer then tests the sensor coil response topaired coils at +22.5 and −22.5 degrees from the current virtual axisand selects the virtual axis with the stronger response. This processcontinues for +/−11.25 degrees, +/−5.625 degrees, until the limits ofdrive power resolution are reached. The resulting virtual axis is theaxis of maximum response. The single board computer 68 calculates theoptimum virtual x axis at forty-five degrees from the measured angle formaximum response and calculates the optimum virtual y axis as an angleorthogonal to the virtual x axis.

A selection of the best set of virtual axes can be accomplished with atriplet-coil drive scheme, with programmable power control to the coildrivers for each axis, and with the driver control to selectively invertthe phase of any coil in the triplet x-y-z coil sets 24 a, 24 b, 24 c(see FIG. 15). Here, the single board computer 68 (FIG. 9) has thecapability to select pairs of drive current power settings which steerthe x-y virtual axis of the paired coils from 0 to 90 degrees. Inversionof one of the coil drivers in the pair provides the capability forx-(−y) virtual axis from −90 to 0 degrees. With the addition of thethird coil drive and inversion the single board computer 68 can sweepthe virtual axis 0 to 90 and −90 to 0 degrees in z range. Themicrocomputer selects pairs of current settings output to the x-y pairedcoil driver to sweep the virtual drive axis from 0 to 90 degrees whilerecording the sensor coil response and this process is repeated with they coil driver phase inverted to sweep from −90 to 0 degrees. The angleof the x-y virtual axis when the sensor coil response data is maximumindicates the sensor coil 30 (FIG. 1) is parallel for the x-y plane. Thesingle board computer 68 then sets this x-y axis and sweeps the z axisdrive from −90 to 0 and 0 to 90 degrees while recording the sensor coilresponse. The polar angle of the x-y-z virtual axis when the sensor coilresponse data is at maximum indicates the sensor coil 30 is parallel tothis virtual x-y-z axis. The single board computer 68 then repeats thisprocess to find the minimum sensor coil response sweeping x, y, and zaxes. The polar angle of the x-y-z virtual axis when the sensor coilresponse data is minimum indicates the sensor coil 30 is perpendicularto this virtual x-y-z axis. These two vectors, virtual minimum andvirtual maximum, define a plane intersecting the sensor coil 30. Foroptimum response, the single board computer 68 calculates a virtual xaxis 45 degrees between the maximum and minimum vectors, then calculatesthe virtual y axis as 90 degrees from the virtual x in the plane definedpreviously. Here virtual z axis is defined as orthogonal to the plane ofvirtual minimum and virtual maximum vectors. The single board computer68 then tilts the virtual z axis and the plane of virtual x axis andvirtual y axis 45 degrees toward the virtual minimum vector, and theresult is the optimal virtual axis set which maximizes the sensor coilresponse. As all x-y-z coil sets 24 a, 24 b, 24 c are mechanicallyaligned the solution for best virtual axes in one corner applies to allcorners in the driver array. The single board computer 68 measures thesensor coil response for all corners using these optimum virtual x, y,and z axes. The sum of (virtual x)², (virtual y)², and (virtual z)²sensor coil responses for each corner may be used to calculate thesensor coil 30 using the trilateration method described in the aboveequations. One method to maintain the optimum x-y-z axis over time is tocontinuously test the sensor coil response to small deviations (offsetangle) from the optimum axis (see FIG. 16 c). Here, the single boardcomputer 68 compares the sum of (virtual x)², (virtual y)², and (virtualz)² sensor coil responses for the current virtual axis to the sum forvirtual axis plus offset angle and the sum for virtual axis minus offsetangle. The computer 68 then selects the axis with the largest summedresponse—this becomes the new optimum x-y-z axis and the processcontinues to iterate testing small deviations over time.

The single board computer 68 may then graphically display the sensorcoil position on the display 22 of the control box 20. The position iscontinuously updated adding onto the previous graphical data to create atrack or path of the sensor coil 30 over time. The user interface of thesingle board computer 68 allows the user to clear the recorded track orto save the recorded track to non-volatile memory. Touchscreens havebeen described; however keyboard or other data input, or user interfaceoptions may be used.

The construction details above for the control box 20 (FIGS. 1, 7) mayprovide for a tethered device with the display/control separate from thepatient block 36, 60 (FIGS. 1 and 7). However, an alternativeconstruction would be to build a device or system in which the patientblock 36, 60 is battery-powered and connected wirelessly to the controlbox 20. In another variation, the control box 20 could be integratedinto or as part of the patient block and placed on the patient chest orother locations to track medical device position. Wireless and/or wiredconnections are thus optionally available for the connections of thedrive coil sets to the control or system components for the drivingthereof; as well as for the connections of the sensor coil to thecontrol or system components for measuring or receiving the responsesignals of the sensor coil.

An alternative construction would be to use four or more drive coils 24oriented as a square, rectangle, pentagon, circle, oval, geometric, orany other suitable shape, in or as the patient drive block 36, 60 (FIGS.1, 7).

An alternative construction (FIG. 7) is to optionally incorporateelectrocardiograph (ECG) monitoring into the medical device locationsystem to facilitate placement of the medical device with sensor coil 30in close proximity to the heart. Here the patient drive block 60 may bemodified with one or more ECG pads 64 and ECG lead wires 62 which attachto the patient's chest and the third ECG lead is provided by aconductive wire 52 added in or otherwise made part of the core of theguide wire or stylet sensor coil 30.

An ECG amplifier can be added to the main interface board 70 (FIG. 9),and the single board computer 68 may then present the ECG on the display22 as the medical device such as a catheter is advanced within thepatient's or subject's body. The user can observe changes in the P-waveor other wave elements of the ECG as the medical device/catheter reachesthe heart. Ideally, the single board computer 68 could use a waveformanalysis to assist the user in recognizing changes occurring to theP-wave or other waveforms.

A component to this design may include connecting the signals from thesensor coil 30 and ECG 52 to the user control box 20. This iscomplicated in practice by covering the entire patient and patient block60 with sterile drapes for insertion of the patient's medicaldevice/catheter. In this design, a miniature stereo phone plug orsimilar could be used to pierce a plastic bag and connect to cable 34,54 a pigtail from the user control box 20.

Methods, devices and systems can thus be provided for one or both oftwo- or three-dimensional location of the disposition of a sensor coilin a subject including: an array of electromagnetic drive coil sets,each set having two or three dimensionally oriented drive coils; asensor coil being electromagnetically communicative with the array ofelectromagnetic drive coil sets; and, a system controller communicativewith and adapted to energize one or more of the electromagnetic coils inthe array of electromagnetic drive coil sets, the energizing of the oneor more of the electromagnetic coils including one or more of energizingthe coils singly, or in pairs of x-y and y-z or x-z coils whilemeasuring the response of the sensor coil; whereby the system uses themeasurements of the responses of the sensor coil to calculate thelocation and orientation of the sensor coil relative to said drive coilsets.

This may include two- and/or three-dimensional location of a catheter intissue using an array of x-y or x-y-z oriented electromagnetic coils,where a sensor coil can be associated with one or more catheter tips,and where the system controller can energize one or more external coils,such as but not limited to, pairs of x-y and y-z or x-z coils whilemeasuring the response of the sensor coil; the system can use thesesensor coil measurements to calculate the position and orientation ofthe catheter tip, and in some implementations, the system controller cangraphically display the catheter tip position, depth and/or orientation,e.g., but not limited to, over time.

From the foregoing, it is readily apparent that new and usefulimplementations of the present systems, apparatuses and/or methods havebeen herein described and illustrated which fulfill numerous desideratain remarkably unexpected fashions. It is, of course, understood thatsuch modifications, alterations and adaptations as can readily occur tothe artisan confronted with this disclosure are intended within thespirit of this disclosure which is limited only by the scope of theclaims appended hereto.

1. A medical device locating system for determining disposition of asensor coil in a subject, said system comprising: a. an array of threeor more triplet drive coil sets, each drive coil set including at leastthree discrete drive coils, each of the discrete drive coils beingelectromagnetic coils; b. at least one sensor coil adapted to provideone or more sensor coil response signals; c. a first system componentthat provides AC drive signals energizing said discrete drive coils;wherein the provision of drive signals includes one or both: (i)sequentially driving one or a pair or a triplet of said discrete drivecoils within a triplet drive coil set; and (ii) selectively providingphase inversion of the drive signal to any one, two or three of saiddiscrete drive coils within a triplet drive coil set; d. a second systemcomponent for measuring resulting one or more sensor coil responsesignals, including one or more of sequential single, paired or tripletsensor coil response signals; and e. a computing component forcalculating sensor coil disposition in the subject relative to saidtriplet drive coil sets from one or more measured resulting sensor coilresponse signals.
 2. A system according to claim 1, further comprising adisplay that shows the disposition of said sensor coil in said subjectrelative to the array of said triplet drive coil sets.
 3. A systemaccording to claim 2, wherein said display displays said disposition ofsaid sensor coil in said subject indicating height, width, and/or depthin said subject relative to the array of said triplet drive coil sets.4. A system according to claim 2, wherein said display displays saiddisposition of said sensor coil in said subject indicating orientationangularly as a graphical angle relative to the array of said tripletdrive coil sets.
 5. A system according to claim 1, wherein saiddisposition of said sensor coil is provided as the location of saidsensor coil in said subject indicating height, width, and/or depth insaid subject relative to said triplet drive coil sets.
 6. A systemaccording to claim 1, wherein said disposition of said sensor coil isprovided as the angular orientation of said sensor coil in said subjectrelative to said triplet drive coil sets.
 7. A system according to claim1, wherein said computing component calculates the disposition of thesensor coil relative to the respective locations of said triplet drivecoil sets using an intersection of spheres.
 8. A system according toclaim 1, wherein said computing component: calculates sensor coil signaldata sets generated from the measured resulting sensor coil responsesignals; selects optimum sensor coil signal data sets from thecalculated sensor coil signal data sets based on the sum of measuredsquared sensor coil data terms that have relatively higher values; usessaid optimum sensor coil data sets in calculating the intersection ofspheres to provide the disposition of the sensor coil relative to therespective locations of the three or more triplet drive coil sets.
 9. Asystem according to claim 1, wherein said discrete drive coils withinone or more of the triplet drive coil sets are disposed in an orthogonalarray.
 10. A system according to claim 1, wherein said discrete drivecoils are arranged in perpendicular axes relative to each other in anx-y-z array within each of said triplet drive coil sets; each x, y and zaxis of each of said triplet drive coil sets being arranged in parallelwith the respective x, y and z axes of all other of said triplet drivecoil sets in said array.
 11. A system according to claim 1, wherein saidarray of three or more triplet drive coil sets are disposed in a two- orthree-dimensional geometric array.
 12. A system according to claim 11,including four or more triplet drive coil sets, wherein one or more ofsaid triplet drive coil sets are disposed outside of a plane defined byat least three of said triplet drive coil sets.
 13. A system accordingto claim 1, further comprising a catheter disposed in physicalassociation with said sensor coil.
 14. A system according to claim 13wherein the sensor coil is disposed in physical association with one ofthe distal portion, the end or the tip of said catheter.
 15. A systemaccording to claim 1, further comprising one or more of a guide wire anda stylet disposed in physical association with said sensor coil.
 16. Asystem according to claim 15, wherein the sensor coil is disposed inphysical association with one of the distal portion, the end or the tipof said guide wire or stylet.
 17. A system according to claim 16,wherein a sterile locking fitting is used to lock said guide wire orstylet with the said sensor coil into a position common with one of thedistal portion, the end or the tip of a catheter.
 18. A system accordingto claim 1, further comprising an electrocardiogram (ECG) operablyassociated with said triplet drive coil array wherein the one or moreECG reference leads are placed on said subject and the ECG signal leadis provided by a conductive core wire supporting said sensor coil.
 19. Asystem according to claim 18, further comprising a display to show theECG signal of the subject over time.
 20. A system according to claim 19,wherein said display further displays the P-wave of the subject as thischanges over time in combination with said disposition of said sensorcoil in relationship to the subject's heart.
 21. A system according toclaim 18, further comprising one or more of a catheter, a guide wire anda stylet with said sensor coil being disposed in physical associationtherewith, and further comprising an integrated conductive ECG leadassociated with the sensor coil, the conductive ECG lead providing anelectrical ECG signal.
 22. A system according to claim 1, wherein eachof said triplet drive coil sets and said sensor coil are independentlyconnected to one or more of said first and second system components byone, or the other or both of wired or wireless interfaces.
 23. A systemaccording to claim 1, wherein one or more the first and second systemcomponents and said computing component are connected by one, or theother or both of wired or wireless interfaces.
 24. A system according toclaim 1, further comprising a display, and wherein one or more of thefirst and second system components, said computing component and saiddisplay are connected by one, or the other or both of wired or wirelessinterfaces.
 25. A system according to claim 1, wherein said at least onesensor coil is connected to at least one demodulator circuit within oneor more of said the first and second system components, and saiddemodulator circuit comprises at least one demodulator for measuring theamplitude of said sensor coil output signals to provide demodulatedsensor coil signals.
 26. A system according to claim 25, furthercomprising an automatic gain control (AGC) circuit connected to saiddemodulator circuit, and said automatic gain control circuit associatedwith and receiving one or more response signals from the sensor coil,the automatic gain control circuit maximizing the response signal beforecommunicating said response signal to said demodulator circuit.
 27. Asystem according to claim 1, further comprising an automatic gaincontrol (AGC) circuit within one or more of said first and second systemcomponents, and said automatic gain control circuit associated with andreceiving one or more response signals from the sensor coil, theautomatic gain control circuit maximizing the response signal beforecommunicating said response signal to said one or more of said systemcomponents.
 28. A system according to claim 1, further comprising a usercontrol box to which connected are said triplet drive coil sets and saidsensor coil.
 29. A system according to claim 28 wherein the user controlbox comprises a programmable computer such that the user control box isprogrammable or adjustable.
 30. A system according to claim 1, whereinsaid first system component further comprises the provision tocontinually adjust or program the intensity or power of current runningthrough one or more said discrete drive coils in at least one or more ofsaid triplet drive coil sets.
 31. A system according to claim 28 whereinthe user control box comprises a display.
 32. A system according toclaim 28 further comprising a subject block in which are disposed one ormore of said triplet drive coil sets.
 33. A system according to claim 1,further comprising (i) an x-axis tilt meter and y-axis tilt meter whichuse gravity to measure the x-axis and y-axis tilt from true vertical;and (2) a computer to calculate and display said location of said tip asheight, width, and depth of the sensor coil corrected for the tilt saidarray of triplet drive coil sets.
 34. A medical device system forlocating the disposition of a sensor coil in a subject, the systemcomprising: a. three or more triplet drive coil sets, each comprising atleast three drive coils, said triplet drive coil sets placed in a two-or three-dimensional geometric array relative to each other; b. at leastone sensor coil; c. one or more system components for: (i) sequentiallydriving one or a pair or a triplet of said drive coils within a tripletdrive coil set; and (ii) selectively providing phase inversion of thedrive signal to any one or a pair or a triplet of drive coils energizingdrive coils singly and then as virtual pairs or virtual triplets, and(iii) for measuring resulting single, paired or triplet sensor coilsignals; and d. a computing component for calculating the disposition ofthe sensor coil relative to the three or more triplet drive coil sets.35. The system of claim 34 wherein the computing component; calculatessensor coil signal data sets generated from said single and paired andtriplet sensor coil signals; selects optimum sensor coil signal datasets from said calculated sensor coil signal data sets based on the sumof measured squared sensor coil data terms that have relatively highervalues; and, calculates the distance of the sensor coil from three ormore triplet drive coil set locations using said optimum sensor coildata sets calculated using intersection of the spheres to provide adisposition of said sensor coil in space relative to the disposition ofsaid three or more of triplet drive coil sets.